This invention relates to positioning devices for machining apparatus, such as laser beam machining apparatus, and more particularly to high-speed high-precision positioning devices with a long position adjustment stroke.
FIG. 1 is a schematic view of a conventional positioning device for a machining apparatus silimar to that disclosed in Japanese Laid-Open Patent Application (Kokai) No. 63-300837. The device of FIG. 1 comprises a coarse and a fine adjustment mechanism to realize high-speed high-precision positioning. Thus, a coarse adjustment table 2 is translated on a bottom base 1 via a motor 3 driving a ball thread 4. Further, a fine adjustment table 5 carrying a work 8 thereon is translated on the coarse adjustment table 2 via another motor 6 driving a ball thread 7. A machining head 9 is fixedly supported on a top base 10 above the work 8.
The method of operation of the device of FIG. 1 is as follows. The coarse adjustment table 2 is driven linearly relative to the bottom base 1 via the ball thread 4 driven by the motor 3. Further, the fine adjustment table 5 is driven linearly relative to the coarse adjustment table 2 via the ball thread 7 driven by the motor 6. Thus, the work 8 is translated with respect to the fixed machining head 9 by a linear distance equal to the sum of the translation of the coarse adjustment table 2 relative to the base 1 and the translation of the fine adjustment table 5 relative to the coarse adjustment table 2. The lead of the thread 7 is selected smaller than that of the thread 4 such that a rough adjustment of the work 8 is effected via the rough adjustment table 2, while a fine adjustment is effected via the fine adjustment table 5. Thus, a rapid and precise positioning of the work 8 is realized.
FIG. 2 shows another conventional positioning device for a laser machining apparatus, which is disclosed in a brochure: "Mitsubishi Carbon Dioxide Gas Laser Machining Device", March 1989, of Mitsubishi Denki Kabushiki Kaisha. The device is capable of adjusting the relative position of the machining head with respect to the work in three mutually perpendicular directions X, Y, and Z. (The X- and the Y-axes represent mutually perpendicular horizontal directions, while the Z-axis represents the vertical direction.) Thus, a table 30 carrying the work 8 is translated in the direction X by the X-axis driving mechanism 31. On the other hand, the machining head 9, radiating a machining beam 16 is carried on a Y-axis directional driving mechanism 32 via a Z-axis directional driving mechanism 33, such that the head 9 may be moved along the directions of the Y- and the Z-axes. The Y-axis driving mechanism 32 drives and translates along the direction of the Y-axis and the Z-axis mechanism 33 and the head 9, while the Z-axis driving mechanism drives and translates the head 9 along the direction of the Z-axis. Thus, the head 9 can be moved in three dimensions relative to the work 8. The respective driving mechanism 31, 32, and 33 are controlled to target positions by a servo control system.
The devices of FIGS. 1 and 2, however, have this disadvantage: Since the inertial load on the driving mechanism is great, high-speed high-precision positioning is difficult to accomplish. In the case of the device of FIG. 1, the work 8 and the fine adjustment table 5 constitute an inertial load for the motor 6, while the work 8, the fine adjustment table 5 and the coarse adjustment table 2 constitute an inertial load for the motor 3. Both loads are large, especially in the case where the weight of the load 8 is large. Thus, in the case where relative position of the work 8 with respect to the head 9 must be adjusted at a high-speed, the movement of the work 8 cannot follow the command value closely, due to the large inertia of the load on the driving mechanism. In the case of the device of FIG. 2, the table 30 and the work 8 constitute an inertial load for the X-axis driving mechanism 31, and the Z-axis mechanism 33 and the head 9 constitute an inertial load for the Y-axis mechanism. Both loads are extremely large, such that when relative position of the work 8 with respect to the head 9 is to be adjusted at a high-speed, the movement of the work 8 and the head 9 cannot follow the command values closely, due to the large inertia of the loads on the driving mechanisms. Thus, both in the case of the devices of FIGS. 1 and 2, it is necessary to drive the work or the head slowly in order to accomplish an enhanced precision. This greatly reduces the machining efficiency.